The present invention relates generally to the field of laser materials processing, and more particularly to technologies related to laser cutting and drilling of semiconductor materials and glass.
Semiconductor Wafer Dicing
Presently, the thickness of the most widely used semiconductor wafers exceeds 200 micrometers. Such thick wafers can be diced using mechanical methods. There are three prevalent methods for mechanical dicing of the semiconductor wafer: diamond saw cutting, scribing and cleaving, and laser cutting. Currently, the majority of wafers are cut using a diamond saw. Scribing and cleaving is utilized only in small volume production, and mainly for diode manufacturing. Laser cutting has not yet been implemented, to the knowledge of the inventor, in any industrial application.
During the process of diamond saw cutting, multiple cracks are always produced in the wafer. The cracks must be removed by chemical etching. This technological step increases the cost of semiconductor chip manufacturing, and has a significant effect on the environment. The rate of diamond saw cutting is proportional to the semiconductor wafer thickness, and cutting of wafers thinner than 50 micrometers is impossible using a diamond saw.
Scribing and cleaving of semiconductor wafers, similar to diamond saw dicing, can be used only for thick wafers. Additionally, cleaving produces a certain amount of scrap due to chipping of the edges of the cleaved wafer, which increases production cost.
The evolution of semiconductor chip manufacturing requires the thickness of the chips to be decreased below 100 micrometers in order to satisfy demands for miniaturization, reduced thermal resistivity providing more effective cooling, reduction of thermal stress effect, and improvement of electrical performance. Therefore, a significant interest has been generated in laser machining technology, which provides contactless cutting and, therefore, can be applied for the dicing of very thin wafers. However, the efforts to implement laser cutting methods thus far have been daunting. In spite of multiple attempts conducted within the industry, beginning with the invention of commercial lasers in the 1960's, the laser machining of semiconductors and glass remains unimplemented in industry. The main challenges are: 1) the high cost of dicing due to the high cost of laser systems and slow laser cutting rates, 2) micro-cracking because of thermal stress induced in the workpiece as a result of the absorption of laser beam energy, and 3) contamination of the surface of the material being cut with melt droplets, due to melt sputtering, which fuse to the substrate material.
Glass Cutting
Presently, the cutting of glass is performed using two state of the art methods. The first of these methods requires mechanical scribing of the glass along a desired cutting line, and subsequent breaking of the glass along the scribe line. The second method is to induce a crack along a desired cutting line on the glass using a laser beam, and then breaking the glass along this crack. The first method is less expensive but produces powder debris during the scribing step. The largest market utilizing glass cutting is flat panel display manufacturing, which is intolerant of the generation of debris. Thus, the second laser cutting method is more promising. Unfortunately, current laser induced thermal cracking cutting methods as described above are applicable only to produce straight cuts or cuts with a large radius of curvature.